Current procedures for fitting hearing aids for children are inaccurate if unaided thresholds (whether behavioral or electrophysiologic) are unreliable, incomplete, or lack frequency specificity. This is a common occurrence with infants, young children, difficult-to-test patients, and patients with profound impairments. Unfortunately, assessments of speech detection and discrimination abilities with and without hearing aids are difficult to obtain in many infants and very young children. Electrophysiologic measures can provide an index of these patients' performance using amplification, which would be valuable for subsequent rehabilitative decisions and monitoring of auditory development and/or therapies. The cortical auditory event-related potentials (ERP), unlike the auditory brainstem response (ABR), reflect the higher level processing of acoustic stimuli, including complex stimuli such as speech sounds, and the brain processes underlying auditory discrimination capabilities. The cortical ERPs are therefore well-suited as probes of a hearing-impaired child's auditory capabilities as well of changes in this performance with use of hearing aids. The objectives of this project are to investigate the cortical auditory ERPs as electrophysiologic probes of stimulus audibility and discrimination in real and simulated hearing loss and with the use of prescribed hearing aids. In addition to investigating the potential clinical application of cortical ERPs, it is expected these studies of the N1-MMN-N2-P3 cortical auditory ERP sequence will provide insight concerning the underlying brain processes altered by hearing loss and amplification.